In the past, various techniques have been developed for the purpose of sterilizing or decontaminating biological sludges and wastes. The most common process is the process of mixing lime with the sludge. The reaction of lime with the water in the sludge serves to elevate the temperature of the sludge to a maximum of 100.degree. C.
In the past, various U.S. patents have issued relating to processes for the decontamination and treatment of wastewater sludges. For example, U.S. Pat. No. 4,038,180, issued on Jul. 26, 1977 to N. K. Talbert, describes a process of dewatering sewage sludge in which the sludge from a municipal or industrial sewage treatment facility is mixed with a mineral acid or anhydride thereof to release the entrapped water in the sludge. The resulting mixture of the sludge solids and diluted acid or anhydride is then mixed with a basic material, such as ammonia, such that the heat generated by the reaction of the base and the acid evaporates the water to form either a completely dry mixture of sludge solids and a salt or a mixture having a predetermined moisture content which may be air dried.
U.S. Pat. No. 4,500,428, issued on Feb. 19, 1985 to Lynch et al., describes a method for the treatment of a wastewater sludge using a pair of reaction vessels, sequentially, to treat the sludge. Both of the vessels are pressurized. The first vessel has an aerator for aerating the sludge. This vesl receives sulfuric acid and chlorine therein through a port. A dewatering device is provided upstream of the first vessel. The outlet of the first vessel is coupled to an inlet of the second vessel through another dewatering device. The second vessel creates a final-treatment chamber in which the sludge is exposed to ozone, air and lime.
U.S. Pat. Nos. 4,781,842 and 4,902,431, issued to Nicholson, teach processes for the decontaminating of wastewater sludges to a level which meets or exceeds U.S. E.P.A. process standards. The process mixes sludge with an alkaline material sufficient to raise the pH of the end product to 12 or higher for at least one day. This process will raise the temperature to 50.degree. C., but will not sterilize the sludge nor does it eliminate the pathogenic organisms.
U.S. Pat. No. 4,306,978, issued to Wurtz, relates to a process of lime stabilization of wastewater treatment plant sludge. This patent discloses the dewatering of the sludge and intimately mixing calcium oxide to raise the temperature so as to produce a stabilized sludge particle.
U.S. Pat. No. 5,482,528, issued on Jan. 9, 1996 to Angell et al., teaches a pathogenic waste treatment process for the processing of solid waste and for the converting of such solid waste into useful products. This is accomplished by combining the waste with an acid, such as concentrated sulfuric acid, and a base, such as fly ash. These exothermically react and thermally pasteurize the waste and add mineral value to the product. Pozzolanic materials, such as fly ash, agglomerate the product. The calcium oxide in the fly ash reacts with sulfuric acid to form calcium sulfate dihydrate.
None of these prior art patented processes are capable of achieving temperatures, when mixed with the sludge, of greater than 100.degree. C. None of the prior art techniques allow for the shorter drying times as required by 40 C.F.R. Subchapter 0, Part 503.32.
U.S. Pat. No. 5,635,069 issued on Jun. 3, 1997 to the present inventors. This patent described a process for treating a waste sludge of biological solids which included the steps of mixing the sludge with an oxide-containing chemical and sulfamic acid so as to elevate the temperature of the sludge, pressurizing the mixed sludge to a pressure of greater than 14.7 p.s.i.a., and discharging the pressurized mixed sludge. The oxide-containing chemical could be either calcium oxide, potassium oxide, or potassium hydroxide. The sludge has a water content of between 5 and 85 percent. The oxide-containing chemical and the acid are reacted with the sludge so as to elevate the temperature of the sludge to between 50.degree. C. and 450.degree. C. The pressurized mixed sludge is flashed across a restricting orifice or passed into a chamber having a lower pressure. The evaporated liquid component can be condensed and used as part of the process or external of the process.
Typically, there are various problems associated with the treatment of sewage. It is fundamental that the sewage be aerated so that the aerobic microorganisms can be suitably supplied with oxygen such that they can consume the waste. In municipal applications, very large aerator assemblies are provided which continually bubble airthrough the sewage. It is desirable to introduce as much oxygen as possible into the liquid of the sewage. Through bubbling air techniques, a maximum of 9 parts per million of dissolved oxygen can be achieved in the liquid at about 75.degree. F. Frequently, the oxygen content of the liquid will fall to such a level that the process becomes anaerobic. Under such circumstances, a horrible smell will be emitted by the waste processing facility. Since these municipal systems are open to the environment, when the process becomes anaerobic, there will be serious complaints by neighboring residents. Furthermore, these open top municipal treatment systems introduce enormous amounts of carbon dioxide and other hazardous air pollutants into the environment. The aerobic microorganisms consume the waste by converting it into carbon dioxide. Some of this carbon dioxide is emitted into the environment. This can exacerbate the "greenhouse effect".
The metabolic rate of the aerobic microorganisms is only limited by the nutrients (the sewage) and by the oxygen uptake rate. As such, if greater amounts of oxygen could be introduced to the sewage, then the aerobic microorganisms would process the waste with greater rapidity.
The cost for aerating the sewage is enormous. For a five million gallon per day facility, the energy cost for operating the aerators is approximately $80,000 dollars per month. Additionally, there is a relatively large capital cost associated with the installation of such aerating systems. Furthermore, because of the relatively small amount of oxygen that can be mixed into the water of the sewage, the processing facility must take up a considerable area. As a result, sewage is pumped into enormous open top tanks. Ultimately, the processed sewage will be discharged into the environment.
Importantly, there have been significant developments in the creation of artificial blood. Artificial blood is used by the military for emergency use, in place of plasma, in field conditions. This artificial blood is a hydro fluoro ether polymer which contains long carbon chains. Oxygen molecules are connected to these carbon chains by a relatively weak bond. As result, when the artificial blood is passed through the human body, the blood is oxygenated by the substitution of carbon dioxide molecules for the oxygen molecules in the polymer. Since the carbon dioxide is attached to the carbon chains with a weaker bond than the oxygen molecules, the carbon dioxide molecules can be easily removed from the polymer and substituted with oxygen molecules. The carbon dioxide can be removed from the polymer by simply passing oxygen intimately with the polymer. As a result, carbon dioxide will be discharged from the polymer.
This artificial blood, consisting of hydro fluoro ether polymers, is described in U.S. Pat. No. 5,567,765, issued on Oct. 22, 1996 to Moore et al., and in U.S. Pat. No. 5,785,950, issued on Jul. 28, 1998, to Kaufman et al. Each of these patents is owned by Minnesota Mining and Manufacturing Company of St. Paul, Minn. Each of these patents describes highly fluorinated chloro-substituted, non-cyclic organic compounds having 7 to 12 carbon atoms. Importantly, it has been found that this hydro fluoro ether polymers can absorb an excess of 48 percent by weight of oxygen. As such, unlike the 9 parts per million achieved through the use of bubbling air through sewage, hydro fluoro etherpolymers can contain approximately 480,000 parts permillion of oxygen.
It is an object of the present invention to provide a process for treating sewage which maximizes the amount of oxygen available to the aerobic microorganisms.
It is another object of the present invention to provide a process for treating sewage which causes a processing of the sewage as completely and rapidly as possible.
It is a further object of the present invention to provide a process for treating sewage which allows the treatment process to be carried out in a closed container.
It is a further object of the present invention to provide a process for treating sewage which eliminates the need for aerators in the sewage tank.
It is still a further object of the present invention to provide a process for treating sewage which allows for the containment of carbon dioxide and other hazardous air pollutants.
It is still a further object of the present invention to provide a process for treating sewage which minimizes the capital and operating costs associated with the treatment of such sewage.
It is still a further object of the present invention to provide a process which renders the sewage pathogen-free and vector-free.
It is another object of the present invention to provide a process that converts the biological waste sludge into a sellable end product.
It is still a further object of the present invention to provide a process for the treatment of sewage that is cost effective, easy to use and easy to install.
These and other objects and advantages of the present invention will become apparent from a reading of the attached specification and appended claims.